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Dielectric elastomer sensors (DESs) have been known as highly stretchable strain sensors for about two decades. They are composite films consisting of alternating dielectric and electrode layers. Their electrical capacitance between the electrodes is enhanced upon stretching. In this paper, a variety of advanced designs of DESs is introduced. An explanation of how these sensors work and how they perform in terms of capacitance versus deformation or load force is provided. Moreover, the paper describes how the sensor design affects the sensor characteristics in order to achieve a high measuring sensitivity. The most relevant quantities to be measured are distance variations or elongations, forces and pressure loads. It is demonstrated that the sensor design can be supported by Finite Element Method (FEM) simulations. In the second part of the paper, possible applications of the advanced DESs are outlined. Pure sensor applications to detect or monitor pressure or deformation are distinguished from other applications, where sensors form a part of a human–machine interface (HMI). DESs are predestined to be used in contact with the human body due to their softness and flexibility. In the case of an HMI, a dosed load on a sensor by the user's hand enables the remote control of arbitrary technical functions. This can preferably be realized with an operating glove, which exhibits different categories of DESs. Possible applications of DESs are described with the support of functional demonstrators. [ABSTRACT FROM AUTHOR]

The resolution of a quartz crystal microbalance (QCM) is particularly crucial for gas sensor applications where low concentrations are detected. This resolution can be improved by increasing the effective surface of QCM electrodes and, thereby, enhancing their sensitivity. For this purpose, various researchers have investigated the use of micro-structured materials with promising results. Herein, we propose the use of easy-to-manufacture metal blacks that are highly structured even on a nanoscale level and thus provide more bonding sites for gas analytes. Two different black metals with thicknesses of 280 nm, black aluminum (B-Al) and black gold (B-Au), were deposited onto the sensor surface to improve the sensitivity following the Sauerbrey equation. Both layers present a high surface roughness due to their cauliflower morphology structure. A high response (i.e., resonant frequency shift) of these QCM sensors coated with a black metal layer was obtained. Two gaseous analytes, H2O vapor and EtOH vapor, at different concentrations, are tested, and a distinct improvement of sensitivity is observed for the QCM sensors coated with a black metal layer compared to the blank ones, without strong side effects on resonance frequency stability or mechanical quality factor. An approximately 10 times higher sensitivity to EtOH gas is reported for the QCM coated with a black gold layer compared to the blank QCM sensor. [ABSTRACT FROM AUTHOR]

This article presents a highly digital robust voltage-controlled oscillator (VCO)-based front end for multiplexed single-ended resistive sensor readout applications. The architecture features a modified digital phase-locked loop (DPLL) structure that enables second-order noise shaping without any operational transconductance amplifiers (OTAs) and a single feedback digital-to-analog converter (DAC). The direct conversion of the sensor input resistance to time-domain information obviates the need for any conditioning circuit, thus resulting in a highly digital and area-compact architecture. The closed loop substantially reduces the amplitude of the signal at the VCO input, thereby achieving high linearity. To ensure high robustness against supply and temperature variations, a double measurement approach is employed. Fabricated in a 180-nm CMOS process with a 0.1-mm2 active area, the sensor readout consumes 109 $\mu \text{W}$ of power and achieves a resolution of 96.9 dB for 0.5-ms conversion time, resulting in a Schreier figure of merit (FoM) of 166.5 dB. The circuit only requires a cheap and efficient single-point trimming calibration at room temperature. The low conversion time enables multiplexing among multiple sensor readouts. The supply and temperature sensitivities are 0.4%/V and 36 ppm/°C, respectively. [ABSTRACT FROM AUTHOR]

Recently there has been a significant increase in demand for wireless sensor networks, as their field of application is rapidly expanding, driven mostly by the growing importance and prevalence of the Internet of Things concept. To enable practical application of wireless sensor networks, sensor nodes must be inexpensive, small, light-weight, intelligent and autonomous. This paper presents a review of low-power always-on wake-up detectors used to reduce a sensor node’s power consumption and enable continuous detection of sparse events. We describe the wake-up concept, discuss its advantages and present the wake-up detector’s power consumption, detection accuracy and false positive rate as parameters of interest. We present a state-of-the-art analysis of wake-up detectors, grouping them based on their power consumption into zero-power and near-zero-power detectors and active detectors, which we further separate based on their implementation into digital detectors and mixed-signal and analog detectors. This analysis shows state-of-the-art wake-up detectors operate with detection accuracy over 90% and a wide range of power consumptions, spanning from a few nW to few tens of $\mu \text{W}$ , because of their diverse applications and sensor modalities. Additionally, it shows that active mixed-signal wake-up detectors are currently the most utilized implementation, with emphasis on acoustic transducer modality. It also shows potential trends for future detector design utilizing more MEMS and NEMS to further lower detector power consumption. We also show techniques and ideas not yet integrated in the wake-up concept, to potentially improve the wake-up detector concept and present the wake-up detectors’ common applications and their specifics. [ABSTRACT FROM AUTHOR]

In the present study, a Schiff base (E)-2-[(3,5-bis(trifluoromethyl)phenylimino)methyl]-4,6-dichlorophenol has been synthesized. Its spectroscopic and X-ray single-crystal data have been compared with the results of theoretical calculations based on the DFT method, as well as molecular electrostatic potential (MEP), HOMO and LUMO, and nonlinear optical (NLO) effects. Antimicrobial activity of the compound has been tested against some bacteria and fungi. According to UV-Vis and agarose gel electrophoresis methods, the compound interacts with DNA electrostatically and breaks it oxidatively. Antioxidant activity of the compound measured by the DPPH method, is lower than that of BHT. [ABSTRACT FROM AUTHOR]

A dual-feedback K-band low-noise amplifier (LNA) is presented. This circuit consists of two common-source configurations in series. Its input matching network uses the shunt inductive transformer technique to reduce the chip area and improve noise matching, and uses the transformer technique to improve the gain and isolation. The measured input and output return losses are less than -10 dB at 23 GHz, the isolation is -50 dB, and the gain at 23 GHz is 10.6 dB. This chip is implemented by 0.18 µm CMOS technology and its dimensions are 0.22 mm2. The DC power consumption is 5.4 mW with a supply voltage of 1 V. This amplifier can improve a complete RF front-end for sensor applications. [ABSTRACT FROM AUTHOR]

The installation of heating systems in buildings and monuments not designed to accommodate such facilities poses technical difficulties, particularly where occupancy and hence system use is sporadic, such as in churches, cathedrals, synagogues, mosques and other places of worship. Furthermore, building materials and architecture may detract from system efficiency. An additional difficulty is the source of energy: when monuments are in remote areas, fuels such as natural gas may not be available, although on occasion they may not be used even when they are available. The present study explores the thermal comfort provided by heating systems generally used in Spanish churches: decentralized gas burner system (propane) and centralized air heating systems (natural gas, fuel oil) based on a new monitoring methodology using temperature, relative humidity and airflow sensors. The church at Talamanca de Jarama (fuel oil) delivered the highest thermal comfort based on environmental conditions, whereas the system installed at Algete (natural gas) was the most energy efficient. The requirements of each heating system were assessed relative to the conservation of the desired indoor conditions, considering energy, comfort and æsthetic factors. [ABSTRACT FROM AUTHOR]

This paper presents a voltage-controlled oscillator (VCO) based current to digital converter for sensor readout applications. Second order noise shaping of the quantization error is achieved by using implicit capacitance of the sensor to realize a passive integrator and a VCO-based quantizer. The non-linearity in voltage to frequency conversion of the VCO is tackled by placing the VCO in a loop consisting of a simple digital IIR filter and a passive integrator. The IIR filter provides large gain within the signal bandwidth and suppresses VCO input swing. As a result, non-linearity of the VCO is not exercised, thus greatly improving the proposed architecture's immunity to VCO nonlinearity. The use of a digital filter instead of an analog loop filter eases the design and makes it scaling friendly. Designed for an ambient light sensor application, the proposed circuit achieves 900 pA accuracy over an input current range of 4 \muA. Fabricated in a 0.18 \mum CMOS process, the readout circuit consumes a total of 77.8 \muA current, and occupies an active area of 0.36 mm^2. [ABSTRACT FROM PUBLISHER]

A novel compact plasma sensor applicable for the supervision and control of industrial plasma processes is presented in this contribution. Based on the multipole resonance probe (MRP), the new planar MRP (pMRP) is introduced as a powerful and economical monitoring tool, flush-mounted into the reactor wall. Hence, it can be used for an effective suppression of disturbances of the plasma process itself. Using 3D electromagnetic field simulations with CST Microwave Studio, the pMRP is investigated and challenges as well as prospects of the new sensor design are discussed in detail. Three different sensor versions are presented and compared with the resonance behavior of the MRP. Furthermore, limitations concerning position tolerances are shown and the suitability of the pMRP is proven. Measurements in a double inductive coupled plasma, with argon as process gas and varying excitation powers, demonstrate the suitability of the pMRP for monitoring purposes. [ABSTRACT FROM PUBLISHER]

This article discusses the experiences from the development and deployment of two image-based environmental monitoring sensor applications using an embedded wireless sensor network. Our system uses low-power image sensors and the Tenet general purpose sensing system for tiered embedded wireless sensor networks. It leverages Tenet's built-in support for reliable delivery of high rate sensing data, scalability and its flexible scripting language, which enables mote-side image compression and the ease of deployment. Our first deployment of a pitfall trap monitoring application at the James San Jacinto Mountain Reserve provided us with insights and lessons learned into the deployment of and compression schemes for these embedded wireless imaging systems. Our three month-long deployment of a bird nest monitoring application resulted in over 100,000 images collected from a 19-camera node network deployed over an area of 0.05 square miles, despite highly variable environmental conditions. Our biologists found the on-line, near-real-time access to images to be useful for obtaining data on answering their biological questions. [ABSTRACT FROM AUTHOR]

A moisture sensor based on a composite resonator is used to measure different honey samples, which include imitation honey. The sensor changes its frequency response in accordance with the dielectric permittivity that it detects in the measured samples. Although reflectometry sensors have been used to measure the percentage of moisture in honey for almost a century, counterfeiters have achieved that their apocryphal product is capable of deceiving these kinds of sensors. Metamaterial features of the composite resonators are expected to improve their response when detecting lossy samples such as organic samples. It is also sought that these sensors manage to detect small differences not only in the real parts of the dielectric permitivities of samples but also in their imaginary parts, and, thus, the sensors are able to discern between real honey and slightly altered honey. Effectively, not only was it possible to improve the response of the sensors by using lossy samples but it was also possible to identify counterfeit honey. [ABSTRACT FROM AUTHOR]

Thiols and selenides bind to the surface of gold nanoparticles (AuNPs) and thus provide suitable platforms for the fabrication of sensors. However, the co-existence of adsorbed citrate on the surface of the nanoparticles can influence their functionalization behavior and potentially their sensing performance measured by the extent of particle aggregation. In this study, the functionalization of purchased (7.3 ± 1.2 nm) and in-house prepared AuNPs (13.8 ± 1.2 nm), under the same experimental conditions with either cysteamine (Cys), 3-mercaptopropionic acid (3-MPA), or l-selenocystine (SeCyst) was investigated. 1H-NMR measurements showed distinct citrate signatures on the in-house synthesized citrate-stabilized AuNPs, while no citrate signals were detected on the purchased AuNPs other than evidence of the presence of α-ketoglutaric acid. Carboxylate-containing species attributed to either citrate or α-ketoglutaric acid were identified in all functionalized AuNPs. ATR-FTIR spectroscopy confirmed the functionalization of AuNPs with Cys and 3-MPA, and energy dispersive X-ray (EDX) spectroscopy measurements suggested the formation of SeCyst functionalized AuNPs. Co-adsorption rather than displacement by the functionalizing agents and carboxylate-containing molecules was indicated, which for Cys and SeCyst functionalized AuNPs was also the aggregation limiting factor. In contrast, the behavior of 3-MPA functionalized AuNPs could be attributed to electrostatic repulsions between the functionalized groups. [ABSTRACT FROM AUTHOR]